In energy harvesting, which provides conversion from weak energy in its environment into electric energy using a power generating element such as a solar cell, a thermoelectric generating element, and a piezoelectric element, power output from the power generating element significantly fluctuates depending on environmental conditions. Thus, in general, to buffer fluctuations in power depending on the environmental conditions, temporary accumulation of the power generated by the power generating element in a capacitor is practiced. In addition, voltage output from the power generating element also fluctuates depending on environmental conditions. Thus, use of a DC-DC converter to stabilize voltage to be supplied to a load is practiced.
As related art of DC-DC converters, there is a DC-DC converter that is activated and supplies power to a load via the DC-DC converter when input voltage exceeds predetermined under voltage lock out (UVLO) voltage. However, power generated by the power generating element depends on output voltage of a power generating element. Thus, if the output voltage of the power generating element is inappropriate at a time of activating a DC-DC converter, power supplied to a load runs short, which involves a risk of failure in activating the load.